The star formation rate distribution function of the local Universe

We present total infrared (IR) and ultraviolet (UV) luminosity functions derived from large representative samples of galaxies at z~ 0, selected at IR and UV wavelengths from the Imperial IRAS Faint Source Catalogue redshift data base (IIFSCz) catalogue, and the GALEX All-Sky Imaging Survey (AIS), respectively. We augment these with deep Spitzer and GALEX imaging of galaxies in the 11Mpc Local Volume Legacy (LVL) Survey, allowing us to extend these luminosity functions to lower luminosities (~10⁶L_⊙), and providing good constraints on the slope of the luminosity function at the extreme faint end for the first time. Using conventional star formation prescriptions, we generate from our data the star formation rate (SFR) distribution function for the local Universe. We find that it has a Schechter form, the faint-end slope has a constant value (to the limits of our data) of α=-1.51 ± 0.08 and the 'characteristic' SFR ψis 9.2M_⊙yr^-1. We also show the distribution function of the SFR volume density; we then use this to calculate a value for the total SFR volume density at z~ 0 of 0.025 ± 0.0016M_⊙yr^-1Mpc^-3, of which ~20 per cent is occurring in starbursts. Decomposing the total star formation by infrared luminosity, it can be seen that 9 ± 1 per cent is due to LIRGs, and 0.7 ± 0.2 per cent is occurring in ULIRGs. By comparing UV and IR emission for galaxies in our sample, we also calculate the fraction of star formation occurring in dust-obscured environments, and examine the distribution of dusty star formation: we find a very shallow slope at the highly extincted end, which may be attributable to line-of-sight orientation effects as well as conventional internal extinction.